1. Field of the Invention
The present invention relates a diaphragm such as a cone, a center-cap or the like for use in a loudspeaker.
2. Description of the Related Art
There is known an electro-dynamic type loudspeaker as shown in its sectional view of FIG. 1. Such an electro-dynamic type loudspeaker has a metal back-plate 1 to the center of which a cylindrical magnetizable pole piece 2 is attached and, a ring permanent magnet 3 is attached to the back-plate 1 at the periphery. A ring pole plate 4 is attached to the top of the magnet 3 and surrounds the tope of the pole piece 2 and thus forms a magnetic gap between the pole piece 2 and the pole plate 4. A voice coil bobbin 6 carrying a voice coil 5 is freely inserted to such a magnetic gap. The voice coil bobbin 6 is supported by a compliant dumper 7 having corrugations. The voice coil bobbin 7 is rigidly connected to the center of a cone 8. The cone 8 is provided with a center-cap 9 at the center of the cone 8. The opening periphery of the cone 8 is supported by an edge member 10 which is fixed by a gasket 12 to a rigid frame 11. Lead wires of the voice coil are electrically connected through twist lines 13 to terminals 14 on the side of the frame 11.
There are various diaphragms for the cone 8 for examples, a cone which heat-formed from a base fabric embracing a resin, a cone which heat-formed from a plastic or foamed plastic thin film, a cone which integrally formed with an edge member from the same material and so on. The material of the cone 8 is selected from a natural paper pulp, a synthesized paper pulp, polyimides (hereinafter referred to as PI), polyetherimides (hereinafter referred to as PEI), polyphenylene sulfide (hereinafter referred to as PPS) or the like.
Since the variety of human everyday living expands the places at which the loudspeakers are set up, the variation of performance and durability in the loudspeaker should be widened. For example, the temperature variation of the cabin of a motor vehicle is about -30 to +80 centigrade through one year and, particular its peak temperature may reach 120 centigrade on a dash board or rear-shelf tray exposed directly in a midsummer. Thus the on-vehicle loudspeaker is required in a high thermal resistance. Furthermore, the on-vehicle loudspeaker is also required to be durable against an ultra-violet ray since a deterioration of cone material occurs due to the irradiation of ultra-violet ray. Therefore, a cone material with a high thermal and light resistance is employed. To improve a water resistance of the cone in the on-vehicle loudspeaker, a cone coated with an acrylic resin or cone essentially made of polypropylene resin is employed.
In this way, it is very important to select materials on the thermal, light and water resistance in the designing for a cone of the on-vehicle loudspeaker since it is used under a severe environment in the motor vehicle cabin. Moreover, the sound quality of loudspeaker is demanded by the improvement of digital music source. Accordingly, a cone with a high performance is also demanded.
However, there is a problem in the thermal resistance that the resin diaphragm with a comparatively high internal loss damping objectionable internal vibrations has a low melting point the other resin diaphragm with a high melting point is solid, but its internal loss is insufficient to dampen the objectionable internal vibrations, so that it is difficult to flatten the middle and high ranges in the audio spectrum property of the loudspeaker.